A healthy adult person usually voids 1000-1500 ml of urine every day. The total amount of solid components thereof is 50-70 g. About 25 g of the solid components is inorganic substances mainly composed of sodium chloride, potassium chloride and phosphoric acid, most of which are dissolved in the form of ions. The remains are organic substances mainly composed of urea and uric acid, and slight amounts of sugar and protein also exist therein. The concentrations of sugar and protein in the urine reflect the health conditions of the adult.
The sugar contained in the urine, i.e., glucose is discharged usually at a rate of 0.13-0.5 g per day into the urine. From this figure and the amount of urine, the concentration, i.e., the urine glucose level can be estimated at not more than 50 mg/dl on the average. The corresponding value is several hundred mg/dl, or sometimes as high as several thousand mg/dl. In other words, the value for diabetics can increase by a factor of ten or hundred as compared with the normal value.
On the other hand, the protein contained in urine, i.e., albumin is smaller in amount than glucose, and discharged at the rate of 3-60 mg into the urine. By taking the amount of the urine into account, average concentration is about 6 mg/dl or less. If a kidney is suffered, the albumin concentration reaches 100 mg/dl or more. That is, the value is increased to ten times the normal value or more.
Ordinally, as a conventional method of examining such sugar or protein in the urine, a test paper impregnated with an agent is dipped into the urine and a color reaction thereof is measured by spectrophotometer or the like.
In this method, however, different kinds of test paper were required to use for different items of examination including sugar, protein, etc. Also, a new test paper is required for each test, thereby leading to the disadvantage of a high running cost. Further, automation for labor saving has its own limit.
In addition, in a case of home use, a layman is demanded to set and change the test paper. This process is comparatively annoying and forms a stumbling block to the extension of the domestic use of the urinalysis apparatus.
Now, the conventional polarimeter will be explained. The conventional polarimeter had the problems described below.
An example of the conventional polarimeter is shown in FIG. 20.
In FIG. 20, a light source 121 is configured of a sodium lamp, a band-pass filter, a lens, a slit, etc. for projecting a substantially parallel light composed of a sodium D ray having a wavelength of 589 nm. A polarizer 122 is arranged in the direction of advance of the light projected from the light source 121 in such a position as to transmit only a component in a specific direction, which has a plane of vibration coincident with a transmission axis thereof, of the light projected from the light source 121. A sample cell 123 for holding a specimen is arranged in the direction of advance of the light transmitted through the polarizer 122. Further, an analyzer 124 is arranged, like the polarizer 122, in such a position as to transmit only the component of the light in a specific direction. An analyzer rotator 125 is for rotating the analyzer 124 on an axis parallel with the direction of advance of the light projected from the light source 121 under the control of a computer 127. A light sensor 126 is for detecting the light projected from the light source 121 and transmitted through the polarizer 122, the sample cell 123 and the analyzer 124. The computer 127 controls the analyzer rotator 125 while recording and analyzing a signal from the light sensor 126.
The principle of this conventional example will be explained with reference to FIG. 21. In the figure the abscissa represents the relative angle .theta. formed between the plane of vibration of the light transmitted through the polarizer 122 and the plane of vibration of the light transmitted through the analyzer 126. Herein, .theta. is assumed to take zero when the angle between these two planes of vibration reaches .pi./2, i.e., in the orthogonal nicol state. The ordinate represents an intensity I of the light that has reached the light sensor 126 based on an output signal of the light sensor 126. Herein, the solid line indicates the output signal in the case where the specimen exhibits no optical rotatory power. Under this condition, the relation between .theta. and I is shown by equation (1) mentioned below. Herein, a transmission loss and a reference loss of the s ample cell 123 and the analyzer 122 respectively are ignored. EQU I=T.times.I.sub.O .times.(cos .theta.).sup.2 (1)
where,
T: transmittance of specimen PA1 I.sub.O : intensity of light incident to specimen PA1 As apparent from equation (1), I changes with a change of .theta., i.e., with the rotation of the analyzer 126, so that an extinction point with a minimum I appears for each .pi.. PA1 where PA1 t: time PA1 .vertline..beta..vertline.&lt;&lt;1 PA1 A: measured angle of rotation of the urine [degree], PA1 A.sub.h : maximum value of the angle of rotation presented by the interfering optically active substance [degree], PA1 A.sub.l : minimum value of the angle of rotation presented by interfering optically active substance [degree], PA1 .alpha.: specific angle of rotation of the optically active substance [degree/cm.multidot.dl/kg], and PA1 L: measurement optical path length [cm]. PA1 where PA1 a: rotational angle of the direction of polarization [minute], PA1 V: Verdet's constant of the medium [minute/A], PA1 H: magnetic field [A/m], and PA1 L: propagation distance [m].
In the case where the specimen has an optical rotatory power and its angle of rotation=.alpha., on the other hand, the light intensity is represented by dashed line in FIG. 21 and given by equation (2). EQU I=T.times.I.sub.O .times.{cos(.theta.-.alpha.)}.sup.2 (2)
As seen from this, a specimen having an optical rotatory power, as compared with a specimen having no optical rotatory power, has the angle associated with the extinction point displaced by .alpha.. The angle of rotation can be measured by finding the displacement .alpha. of the angle associated with the extinction point by the computer 127.
In this method, however, S/N ratio of the output signal of the light sensor 126 is comparatively inferior for lack of a modulated component and it is difficult to accurately determine the extinction point. As a result, a specimen with a small .alpha. cannot be measured with high accuracy.
For this reason, a polarimeter shown in FIG. 22 is also used in order to improve an accuracy of determining the extinction point. In FIG. 22, a light source 141 is configured of a sodium lamp, a band-pass filter, a lens, a slit, etc. for projecting a substantially parallel light of sodium D ray having a wavelength of 589 nm. A polarizer 142 and an analyzer 144 are arranged in the direction of advance of the light projected from the light source 141 aligning their transmission axes with the direction of advance of the light projected from the light source 141, with a sample cell holding a specimen interposed therebetween. An analyzer rotator 145 is for rotating the analyzer 144 on the transmission axis thereof as a rotation shaft under the control of a computer 147. A light sensor 146 detects the light projected from the light source 141 and transmitted through the polarizer 142, the sample cell 143 and the analyzer 144. The computer 147 controls the analyzer rotator 145, and records and analyzes the signal of the light sensor 146. An optical Faraday modulator 151 vibrates the direction of polarization. A signal generator 152 drives the optical Faraday modulator 151. A lock-in amplifier 143 is for phase sensitive detection of an output signal of the light sensor 146 with reference to the vibration-modulated signal from the optical Faraday modulator 151.
The operating principle of the polarimeter will be explained below with reference to FIG. 23.
In FIG. 23, the abscissa and the ordinate represent, as same in FIG. 21, .theta. and I, respectively, with the extinction point and the neighborhood thereof shown in an enlarged view. The optical Faraday modulator 151 vibration-modulates the direction of polarization with an amplitude of .delta. and an angular frequency of .omega.. In the process, I is given as shown in equation (3) below from equation (2). EQU I=T.times.I.sub.O .times.{cos(.theta.-.alpha.+.delta..times.sin(.omega..times.t))}.sup.2(3)
In FIG. 23, the extinction point or the neighborhood thereof is involved, i.e., .theta..apprxeq..pi./2, and therefore equation (4) can be approximated as shown by equation (4). EQU .theta..apprxeq..pi./2+.beta. (4)
where,
Substituting this equation (4) into equation (3) gives equation (5) below. EQU I=T.times.I.sub.O .times.{[sin(.beta.-.alpha.+.delta..times.sin(.omega..times.t)]}.sup.2(5)
If it is assumed that an angle of rotation of the specimen and an amplitude of vibration. modulation are small, that is .vertline..alpha..vertline.&lt;&lt;1 and .delta.&lt;&lt;1, equation (5) is approximated as shown in equation (6) below. EQU I.apprxeq.T.times.I.sub.O .times.{.beta.-.alpha.+.delta..times.sin(.omega..times.t)}.sup.2 EQU =T.times.I.sub.O .times.{(.beta.-.alpha.).sup.2 +2.times.(.beta.-.alpha.).times..delta..times.sin(.omega..times.t)+[.delta ..times.sin(.omega..times.t)].sup.2 } EQU =T.times.I.sub.O .times.{(.beta.-.alpha.).sup.2 +2.times.(.beta.-.alpha.).times..delta..times.sin(.omega..times.t)+[.delta ..sup.2 /2.times.(1-cos(2.times..omega..times.t))]} (6)
This indicates that the output signal I of the light sensor contains signal components of angular frequency=O (DC), .omega. and 2.times..omega.. This is obvious also from FIG. 15. By the phase sensitive detection of the value I with the vibration-modulated signal as a reference signal in the lock-in amplifier, it is possible to pick up the component of the angular frequency .omega., i.e., the value S shown in equation (7) below. EQU S=T.times.I.sub.O .times.2.times.(.beta.-.alpha.).times..delta.(7)
This S is zero only when .beta.=.alpha. and this point constitutes an extinction point. In other words, the value of .beta. when S becomes zero in a step of rotating the analyzer and sweeping .beta. is the angle .alpha. of rotation.
As described above, modulation of the direction of polarization, makes it possible to pick up the signal of the modulated frequency component selectively by separating it from noises such as a source light intensity, power fluctuations and radiation, thereby making it possible to obtain the signal S with high S/N. This value S can be used to determine the extinction point accurately and permits a highly accurate measurement of the angle a of rotation.
Nevertheless, the above-mentioned polarimeter is complicated in structure due to the need of a means for rotating the analyzer and a modulator, and therefore has its own limit of cost reduction and reliability.